Valve for use with air blast circuit breaker



Jah. 27, 1948. w. M. "SCOTT, .1R

VALVE FOR USE WITH AIR BLAST CIRCUIT BREAKER 2 Sheets-Sheet 1 Original Filedv Dec.

.LEE-Eig I INVENTOR. bui/man1 771. Mfr.

mw.. l r.. *Il

ATTORNEY.

Jan. 27, 1948.

w. M. sco-r1', .JR 2,435,162

VALVEFOR USE WITH AIR BLAST CIRCUIT BREAKER Original Filed Dec. 21, 1940 2 Sheets-Sheet 2 INVENTOR.

WLMi

ATTORNEY.

Patented Jan. 27, 1948 VALVE FOR 'USE WITH AIR BLAST CIRCUIT BREAKER William Maxwell Scott, Jr., Bryn Mawr, Pa., as-

signor to I. A".l. E. Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsyl- Vania Original application December 21. 1940, Serial No.

371,092, now Patent No. 2,390,966, dated December `11, 1945. YDivided and lthis application January 4, '1944, Serial No. 516,918

l Claim. 1 This invention relates in general to the -feld of circuit interrupters and more specifically con..- cerns a circuit breaker and a control circuit there.- for, particularly adaptable to the protection of mercury arc rectiers and their associated circuits. This application is a division of my parent case Patent No. 2,390,966, issued December 11,

.An object of this invention is to provide a novel valve control mechanism for circuit breakers.

This and other objects Will `become appa-rent from the following specication taken in connection with the accompanying drawings, in which Figure 1 is a broken cross-sectional View of a single pole Circuit 'breaker and the means for interlocking the same with a plurality of similar poles.

Figure la is an enlarged view of part of the circuit breaker shown in Figure 1.

Figure 2 is a fragmentary View `of one of the control switches operable by the circuit breaker taken along the line 2-2 of Figure 1.

The exact nature of the single pole circuit breaker and of the tripping and vcollrel means therefor will new be described and reference is now made to the .crossseetional views of the single pole breaker, Figures 1 and 1a,

The single pole .of the circuit breaker illustrated consists essentially .of two cooperable contacts 3| and 32, ,and means for directing and controlling an air blast which enters through the pipe 33 .and passes over the separated contacts during circuit interrupt-ion. rIhe plurality of circuit breakers which are required for the various rectifier anode leads may all be mounted directly upon a common storage tank to shorten and thus facilitate piping connections thereto, That is. the base .0i the v flange 6.5 may be coupled by bolts er other suitable means directly te an air storage .tank which charged `by means of a compressor. The Systems, 4may be adjusted so that pressure therein :remains within predetermined limits and that any veriatlons of pressure outside of these vli-rnits may operate to open the circuit break-ers- The main .metallic casting `.36 .of the circuit breaker is, as will :hereinafter ehe shown, at a relatiyely high potential and it is thereiore necessary to electrically isolate the casting from ground potential. Therefore, the casting 3B le supported upon the air ,storage tank by vmeans of a pipe 33 made of `a suitable insulating material and of suf- Iicient vlength to ensure a minimurnoi leakage and to preclude the possibility i `all are between the circuit breaker frame and the air storage tank.

The `base of the casting 36 is preferably a eircue lar external fla-nge 31 which is supported upon the pipe and thus upon the air storage tank by means of the piping -flange 4I which is in screw thread eng-agement at 42 with the insulating pipe 33. The external flange 31 of the casting 36 may then be fastened to the piping flange by any con veulent means, as for instance, a plurality of machine screws, but rst an annular gasket 43 is inserted therebetween to preclude the leakage of air at the junction of the surfaces.

A tapered opening 44 of diameter equal to the inner diameter of the insulating pipe 33 admits .to the casting 36 air which is then conducted through the cored passage 45 to the controllable .diaphragm valve 4-6.

The cored passage 4-5 terminates in an annular air passage 41 which completely surrounds the diaphragm valve 46. Aligned with the valve is a projecting circular pipe 5I which provides a passage 52 for directingr the incoming air to the contacts 3| and 32. The end surface 53 of .the inwardly projecting pipe .5l is ,smoothed to cooperate with a layer 54 .of valve seat material which ls carried bythe valve diaphragm 46.

The passage 52, provided by the annular metallic projection 5l which has vbeen integrally molded into the casting 36 spirals to completely surround the contact 37| as lindicated in Figure 1.

Thus, air .entering into the passage 52 will be conducted to the contact 3l and the air stream will completely surround the contact.

Returning now to the air control means, that is, ythe diaphragm valve 45 illustrated in Figure 1, it may be seen that air now in the cored passage 52 is controlled by the position of the valve seat material 54 relative to the edge 53 of the inwardly projecting pipe 5l.

The valve' diaphragm is supported upon the metallic casting `36 in a counter-bored recess k55 in the Wall of the casting. The ,diaphragm 46 is a circular piece oi flexible material such as rubber `and is held in the counterbore 55 by means of a circular dome shaped member 56 which is turned down at 51 to correspond with the inner diameter of the ycounter bore 55.

The dome shaped member 56 is then securely fastened to the main casting 36 by means of a plurality of machine screws `6I which are circularly disposed.

The machine screws 6I Dass through a corresponding set of per-orations .62 in the dome ,shaped .member and engage threaded perforations 63 Within the main casting 36. The valve diaphragm 46 is thus securely clamped between the projection 51 and the main casting 36. In order to assure an air tight joint at this point and to prevent radial movement of the edge of the diaphragm when subjected to air pressure, a wedge shaped circular protrusion 64 on the projection 51 is forced into the resilient material of the diaphragm when the screws 6| are tightened.

The member 56 has been machined to provide the spherical dome 65 and thus axial displacements of the diaphragm 4S are limited to the space between the dome 65 and the end 53 of the inwardly projecting cored pipe 5|. The valve diaphragm 46 is of flexible material and has secured to it two circular metallic disks 66 and 61 on either side of the flexible material. The face of disk 61 is faced with a valve seat material 54 which will provide a suitably close surface engagement with the end 53 of the inwardly projecting passage. The four layers of material therefore which comprise the movable portion of the valve are bound together by the screw 1| and its associated nut 12 which assists in directing the flow of air toward the discharge when the valve is open.

The rear face 14 of the metallic disk 68 has been machined to correspond with the dome shaped chamber 64. Thus it may be seen that the inowing air which enters through the insulating pipe 33 is guided to the annular Vcored passage 41 surrounding the inwardly projecting pipe 5| and the face of the diaphragm valve. If now the diaphragm 46 is displaced to the left, as viewed in Figure 1, the air will, as indicated by the arrow heads of Figure 1, enter from the passage 45 and passage 41 into the tapered and spiralled passage 5'2 which supplies air to the contact engaging surfaces. Therefore, actuation of the diaphragm valve 46 will control the circuit breaker blast and will be discussed in greater detail in later paragraphs inasmuch as the structural details of the circuit breaker will now be described.

Contact 3| is a conically shaped butt contact engageable with a nozzle shaped contact 32 along the contact surfaces 3|' and 32' which have been faced with a suitable contact material such as a. non-welding alloy of tungsten and silver, silver and graphite, or the like.

Nozzle shaped contact 32 is fixed relative to the main frame 36 of the circuit breaker whereas contact 3| is slidable relative thereto. As indicated in Figure 1, contact 3| has been displaced from its closed position and thus the air flow is indicated by the arrow heads. As the blast air approaches the contacts through a spirally shaped passage 52, the air flow about contact 3| will be in the form of a vortex while passing outwardly through nozzle shaped contact 32. Therefore, an arc which is drawn between contact faces 3|' and 32' as a result of contact separation will be spun about the contact surfaces. This action will facilitate cooling and decrease the possibilities of contacts 3| and 32 welding. The spinning air exhausting between the contact surfaces and through contact 32 is illustrated schematically by the arrow heads in Figure l.

Nozzle shaped contact 32 is supported within a circular opening 15 which is formed within a projecting extension 16 of the main casting 36.

As will be pointed out in later paragraphs, the main frame 36 is at the potential of contact 3| and therefore it is necessary to support Contact 32 within the opening 15 by suitable means of insulating material. Contact 32 is secured between the line terminal 11 and the exhaust pipe and muier 8| and 82. This assembly is made rigid by an external flange 83 on the outer end of contact 32 nesting within counterbores 84 in terminals 11 and 85 in exhaust pipe 8| so that when the parts are assembledl as indicated in Figure 1, the contact 32 will be rigidly held therebetween.

The entire assembly is maintained in fixed relation by means of la plurality of studs 86 extending from terminal 71 and passing through corresponding perforations 81 within the flange end of the exhaust pipe 8|.

To serve as additional insulation between the frame 36 and the line terminal 11, a cylindrical tube |03 is cemented to the insulating plate |0| at perforation |04 and is of an outside diameter equal to the inner diameter of the passage 15 in the main frame 36. Therefore, when the contact 32 is secured by means of flange 83 between the line terminal 11 and the exhaust pipe 8| and this entire assembly is subsequently clamped to the main frame as indicated in Figure l, along with the insulating plate |0| and the insulating cylinder |03, contact 32 will project into the passage 15 and will be centrally located with re'- spect to the spirally oriented air passage 52.

It should be noted that the outer cylindrical surface of the contact 32 has been turned down at |05 to provide an air gap |06 between the insulating tube |03 and the face of the contact 32 which is at the potential of line terminal 11. This, in effect, provides an increased leakage path and therefore reduces the possibility of electrical break-down at this point.

The nozzle shaped passage |01 of the contact 32 provides for the expansion of the blast air in order to reduce back pressure.

Exhaust pipe 8|' juxtaposed against contact 32 along the face provides a tapering passage which is a continuation of the tapering passage of the low pressure side of the nozzle. The pipe supports, by means of the screw threads ||2, the hollow cylindrical muiller 82 and the deionizing stack 3. This stack comprises a plurality of parallel metal laminations over which the hot arc products pass and are effectively cooled.

Conical contact 3| is mounted upon a piston ||4 which is slidable within a cylinder 5 in the main casting 36. In order to prevent leakage of air over the piston ||4, a series of grooves |6 have been turned in the piston and piston rings or other packing may be inserted therein.

The contact 3| is centered on the piston ||4 by a boss extending into a perforation ||1 and is clamped thereto by means of the screw threaded plunger rod 2| This rod has been turned down and threaded at the end |22 which engages a tapped perforation in the contact 3|. By tightening these threads, the annular flange |23 is brought into contact with a flexible conductor |24 which has been perforated at |25 to allow the passage of the plunger rod |2|. Therefore, bringing plunger rod |2| into screw thread engagement with the perforation in 3| will securely clamp the assem-bly of contact 3|, piston ||4 and ilexible conductor |24.

The movement of piston ||4 is limited by the engagement of contact faces 3| and 32 at one end of the stroke (at which time the circuit is closed) to the engagement of the rear face of the piston with a ring shaped rubber or other flexible washer |26 which has been secured within a re-entrant ange |21, molded into the main casting 36, the outer edge of this flange being cut away at |3| to allow for the passage of the flexible conductor |24.

.asoman Esto'n di# therefore which is operable within the chamber H15 between the limits ci engagenient with the stationary .Contact and the annuim' rubber ring 126, is the operating element .of the .circuit breaker, .that iis, .operation of the piston 2| Il in either direction by means -oi .air pressure :controlled by diaphragm lvalve 46 or .any of the other valves which will .hereinafter "be discussed, `will operate reither to .open or close the circuit.

Contact 3l is connected to the external vvcircuit 2through the fflexible conductor :|24 which allows movement without lin :any way impe'ding movement of the piston. The flexible conductor .|24 i'sfcomposedfoi afseres .of highly conductive metal llaminations stacked together by 'suitable means and is fastened at either end to a bifurcated member 133.. 'The biiurcated `.member |33 then continues downward to engage the line terrni- 'nal |34 and the cable 135 from the external .circuit by means of the bolt or `other fastening `means 136.

"Supported by the flange .|21 is a member '|4| which positions the lplunger :rod 1'2 The mem ber 345| contains a cylinder 11.42 in which is oper- :4

@A ilange 155 on the plunger rod |2l which 1;...

originally had been machined circular similar to the flange -|'23 is milled off so that it may engage the rectangular cross-'section of a U -shaped channel |55 as indicated in Figure '1.

The piston |113 'is drilled at '|51 vto allow the passage of plunger rod |2| which is then clamped thereto by 'means of the nut |6|. Prior to the application of the nut, however, `a series of fiber yor other type of washers |44 are slipped over the plunger rod |21 and thus when clamped by nut 151 provide the necessary air tight packing for lpiston F43. The lil-shaped channel |56 is held between the ange |55 and the piston |43 `and is allowed to extend out through the axial perioration |562 in member 14| so that it may 'coopcrate with the switching member |53 which will `hereinafter 4'be described.

Contact 3| is biased normally towards the open rposi-tion, that is, the `position corresponding rto contact between the rear oi the piston 4|`|4 and the shock absorbing member |26. This is accomplishedby 'means v oi. a 'compression spring 1| 64 ywhich is lodges between the ire-entrant hangs |54 "ipreviously :described and the ilange `|55 which supports the fUshaped channel. As the spring is normally under compression, and as the re-.entrant flange .|54 .is ixed, there is .a tendency to draw contact .3.1 .from engagement with contact .32.

The outer end of the closing cylinder casting is provided, .at vits lower edge, with .a pair of horizontal lugs |59.. The ""bi'furcated member .133., which is also the over-current 'bus bar, is supported against the bottom of these lugs by studs threaded into the bar, passing through holes in the lugs and held in position by 'nuts and vlock washers |10. The lower end of the bar is braced by 'the member |83 as will be described in a iol- 'iowing paragraph.

The iorkedcondu'ctor |33 supports, upona pro.-

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trusion, the 'plurality pf machine screws 'i111 'which =pass 'through magnet lamlnations i212. The magnet is composed of .stacked .soit iron or `other magnetic laminations each of which is horse-shoe shaped and as such surrounds the magnet bus 'bar |13 which .is :an .integral .extension ofthe :forked member 1'33. 4As vit is desirable to preclude `.the possibility .oi current flowing through the magnet, the screws .|1| are insulated by means oi insulating :sheaths |15 which icom pletely surround their respective screws,

.As indicated in Figure l, the magnet bus .|13 which may, during short circuit periods carry `considerable currents, .is .braced Vso as to preclude any mechanical deformation thereof due to the ystresses 'developed by virtue of the magnetic forces. The brace comprises the metallic member |83 which has been fastened by rnean'sof `ma chine screws 84 to theframe of casing 36 and by means of the plurality 'of machine .screws and bolts |85 tothe magnet bus. This brace is insulated from the iiange 31 by insulating 'layer 1.89; however, the brace itself may be formed from 'an insulating material.

The electromagnetic device |712 in conjunction with the armature Vila` controls the diaphragm valve -4'5 to control the admission of air Lto the foontact 1chamber` The plunger rod |11 operates under the indu-ence of the magnet H2 vand in 'order that 'the rod `1.11 be maintained Y.in aligrr ment, it passes through a perforation |86 within the magnet lamination stack and through a perforation :|81 in `the magnet bus bar |13..

The armature .|15 is 'clamped securely to the vrod `|171 between the .fiange |13 and nut 1| 9| which engages .a vseries of screw threads on rod |11, 'The rod |11 is .continuously biased towards the right as Viewed in Figure 1, by means included 'Within the cylindrical member |93.

The cylindrical member |93 is fastened to the main frame 35 through the dome shaped mein1 `ber 56 by means of the screw threads `L94 upon both Ythe cylindrical member and a corresponding hollow in the rear of `the `idoine shaped member.

However, inserted into the hollow of the dome shaped member prior to the insertion of the hollow cylindrical member 1.93, is a small circular metal piece |95 which contains a conical valve seat |96 and a cylindrical perforation |91 to permit the passage of air from the diaphragm IValve. The conical projection of the circular metal member 95 provides vfor surface engagement with a layer of valve seat .material 20| which is embedded in a metallic disk 2F32 which is integral with the end ofthe rod i171.

The disk 202 is machined to correspond with the inner wall of the .hollow cylindrical member |53 so that it is maintained central at all times,

The hollow cylindrical member |93 is termi :hated rby :a metal stop v2ll3 which is fastened thereto by means of 'the engaging screw threads 2u# 'and `which is `perforateil .centrally .at 205 to pen mit the free operation of rod |11.

It should be lnoted that bearings are provided for-:rod .|11 bythe periorations within thebus bar and in the metal stop `203. The biasing means for rod |11 is obtained by spr-ings .acting between the metal disk 202 and stationary members, Thuis a small diameter Ycentral spring 2&5 bears against both 'the inner race of disk 12oz andthe inner face of the metal stop .203. This spring is .of 'relatively small diameter and fits :over the rod |11 which thus acts as a guide therefor.

.A second .and adjustable :spring .201 .bears against the inner face of the disk 202 and also against a movable or adjustable guide 2| I, The guide 2|| is a ring shaped metallic member haviner a perforation 2|2 of diameter large enough to pass over the spring 286 but small enough to provide a seat for the end of the spring 291. The ring 2| I is slidably fitted within the hollow cylindrical member 93 and is adjusted therein by means of a plurality of fins 2| 3 which project through axial slots 2|4 in the walls of the cylindrical member |93.

These fins may comprise merely two pins which have been embedded in the ring shaped member 2| and project from the axial slots 2|4. As both spring 206 and spring 291 are continuously under compression, there will be a tendency to move disk 292 and its attached rod |11 to the right as viewed in Figure l, The magnitude of this tendency is controllable by means of the adjustable nature of spring 291. That is, by threading the outer surface 2 |5 of the hollow cylindrical mem- -ber |93 and passing a nut 2|5 thereover and in engagement with the threads 2|5, the ns 2|3 may be displaced axially upon rotation of the nut 2|6, Thus the compression of spring 201 will vary with the position of nut 2 6.

Obviously, therefore, the Variation in the compression forces of spring 291 will accordingly vary the biasing force of rod |11 and its associated magnetic armature |15. As will be indicated in the following, the magnet |16 when operated controls the operation of contacts 3| and 32, Accordingly, an adjustment of either the air gap or restraining force on the armature will correspondingly vary the magnetic forces required to displace the same and thus operate the circuit breaker. This then provides an adjustment for the tripping current required.

Two small control switches are actuated by the rods |63 and |11. The switches as more clearly indicated in Figure 2 are mounted upon insulating brackets such as 2|1 and 2|8. The switches operable by their contact carrying rods are essentially butt contact switches employing a metallic bridge to complete the circuit between the two contacts. Thus as indicated in Figure 2, the rod |63 carries the bridging metallic member 22| which is engageable with the two butt contacts 222 and 223.

The rod |53 passes through a perforation 224 within an insulating member 225 and thus is maintained in slidable relation therewith. The entire switch is clamped to the insulating bracket 2|1 by means of the screws and bolts 226.

When the circuit breaker contacts 3| and 32 are closed, switch 22|, 222 is in the open circuit position, On the other hand, when rod |11 is biased so that valve seat material comes into contact with the metallic insertl |95, the switch 23| is in the closed circuit position.

When contacts 3l and 32 are closed, current ows from the bus bar or other electrical connection '235 which is bolted to the line terminal bus 11 by means of the bolts 236e, through the engaged contacts and then through the flexible conductor 24 to the tines of the bifurcated member |33, then through the magnet bus bar |13 andv out through the cable or bus bar |35 fastened thereto.

Under closed circuit conditions and no electrical disturbances, the full tank pressure will exist in the passage 45 and the annular cored chamber 41 on one side of the diaphragm valve 46 and also in the chamber between the valve 46 and the dome shaped member 56. Under these conditions of equalized unit pressure on both sides, the valve 46 will be displaced more to the right as viewed in Figure 1 inasmuch as the left side of the valve has a considerably larger area than the ring-shaped under side of the valve. Therefore, with equal unit pressures on both sidesof the diaphragm, the valve seat material 54 will be forced into engagement with the end of the projecting passage 52 and thus cut olf the supply of air to the involute passage surrounding the contacts.

The contacts 3| and 32 are maintained in engagement allowing full air pressure to be established within the chamber 236 which will thus actuate piston |44 and rod |2| in a direction which will close the contacts against the action oi the biasing compression spring |84. I

However, the removal of valve disk 54 from contact with the projecting pipe 53 will allow full pressure to be built up in the involute passage 52 to the contacts 3| and 32.

From Figure 1, it may be seen that piston |I4 which is fixed relative to contact 3| is of considerably larger diameter than the piston |43 and therefore without necessarily releasing the pressure in the chamber 236, the contact 3| willA be displaced to the left is viewed in Figure 1.

Full tank pressure is maintained in the chamber 235 by means of the closing manifold 231 which connects the air from the storage tank to each of the single pole circuit breakers controlled therefrom. The manifold 231 itself may comprise a Bakelite tubing perforated at 24| to allow the admission of air to and from chamber 236 and the entire manifold is supported between two clamping brackets 242 and 243 which are maintained in xed relation by means of the plurality of bolts 244 which, in addition, fasten the brackets to the frame of the circuit breaker.

When the circuit breaker is connected in circuit with the anodes of the rectifier and all the poles are closed, the individual poles are interconnected by the manifolds 231, and 255, and full tank pressure will exist in both manifolds. Therefore, as full tank pressure also exists in the passage 45 and in the annular chamber 41, the diaphragm 46 will be moved as determined by the side having the greater surface area.

This obviously is the side which is adjacent the dome shaped member 5S as the area of the valve disk covering the blast pipe is at atmospheric pressure. Full tank pressure exists between diaphragm 46 and the inner wall of the member 56 inasmuch as this chamber is connected with the tripping manifold 255 through the duct 264 and the plurality of perforations 265. It should be recalled that for normal conditions of operation (that is, values of current up to the current for which the armature is adjusted) that the valve 29| is normally biased to engagement with the disk and therefore the air within the dome and within the tripping manifold does not escape. Should a fault occur on the anode to which the pole under discussion is connected, the arma'- ture |15 would be actuated to the left as viewed in Figure 1 under the influence of magnet |12, and the valve 29| will be removed from surface engagement with the disk |95.

' This will immediately allow the air contained within the dome to exhaust through the plurality of openings 255 and through the nozzle shaped opening |91. This air will pass to the outer atmosphere through the guide fins around the valve 20| and then through the perforations 2| 4 within the wall of the hollow cylindrical member |93.

In addition to this escape air which is flowing through opening |91, air will ow from the tripping manifold through the duct 264 and out through the opening |91. Inasmuch as this outflowng air is at a high pressure, means must be provided to prevent it from reducing the velocity 110W from the dome through this passage. The aspirating effect has been arranged in order to increase the velocity of the air flowing from the dome. High pressure air cannot enter the dome through the duct 256 because a check valve therein (not shown) effectively blocks any such flow.

A reduction in pressure within the dome will immediately allow the full air pressure contained within the chamber 41 to actuate diaphragm valve 46 to the left as indicated in Figure 1 and accordingly allow the main air blast entering from the tank, upon which the breaker is mounted, to flow into the involute passage 52. The increase in pressure within the passage 52 will operate upon the relatively large diameter piston |14 and will thus force' contact 3| to the left against the action of the high pressure air upon the small diameter piston |43.

Immediately thereafter an arc will be drawn between contacts 3| and 32 which will be extinguished by means of the high velocity air blast which is in this instance a rotating or spinning air blast.

The heated air will exhaust through the nozzle shaped contact 32 and its associated extension 8i. Upon flowing through the muffler 82, the air stream will be cooled by the stack ||3 which, as previously described, comprises a parallel stack of spaced metal plates.

During the operation of the circuit breaker under the influence of an overload or fault current two other important operations are performed in the following sequence. First, upon the actuation of magnet armature |16, the switch 23| is opened, and second, immediately following the displacement of contact 3| to the left, i

the contacts of switch 221 are closed.

The position of the armature |16 is determined by the current flowing through the magnet bus bar |13 and therefore immediately following current interruption, the force upon armature |16 will vanish and therefore the armature |16 will again be solely under the influence of the biasing springs 206 and 201.

The springs will carry the valve disk 20| into engagement with the metallic member |95. It is important to note that the springs 206 and 201 ,must supply sucient biasing force to close the valve although full tank pressure exists within the opening |91. The reclosure of valve 20| will, through ducts 254 and the plurality of openings 265, cause the pressure to the rear of diaphragm 06 to build up to the full tank pressure whereupon the diaphragm valve will immediately close and thus cut off the supply of air flowing through the involute passage 52.

This precaution has been taken, to preclude the possibility of the air stored within the tank from completely discharging through the chamber 52 and its associated exhaust passages. Again, as-

suming that no other external influences have acted upon the circuit breaker, the removal of the air supply from chamber 52 will effectively decrease the pressure therein and accordingly if :the full pressure still exists within the closing manifold 231 air will flow to operate the piston |43 and its associated piston rod |15! to the right as viewed in Figure 1 to close contacts 3l and 32 and thus complete the circuit which had been interrupted by means of the automatic electromagnetic tripping device |12.

The cycle of events described immediately above concerning the operation of the circuit breaker under the iniiuence of an overload assumed that the pressures in the two manifolds 231 and 255 remained at the storage tank value.

It will be evident that many modifications of the abovedescribed circuit breaker design and circuit breaker control systems may be made by those skilled in the art and therefore I do not wish to be limited to the specic disclosures hereinabove set forth but only by the scope of the appended claim.

I claim:

In a control mechanism, a source of compressed air, an air passage, a housing therefor, a valve seat, a second air passage communicating with said source of compressed air and with said rst passage across said valve seat, a valve disc for engaging said seat to prevent flow between said passages, a flexible diaphragm secured to said housing and supporting said valve disc, said diaphragm being movable toward and away from said seat, a member secured to said housing and enclosing the face of the diaphragm opposite said disc to form a dome-shaped space, means for controlling the pressure within said domeshaped space for governing the engagement and disengagement of said valve disc and valve seat comprising a conical control chamber in said member having a discharge opening, a nozzle for discharging air into said chamber toward said opening, said nozzle being coaxial with said discharge opening, a passage from said nozzle to said source of air pressure, a duct between said chamber and said dome-shaped space, and a valve controlled by adjustable electromagnetic means for controlling the flow of air from said discharge opening.

WILLIAM MAXWELL SCOTT, JR.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 971,934 Siegrist Oct. 4, 1910 1,648,126 Hosmer Nov. 8, 1927 1,835,367 McKee Nov. 1, 1932 1,901,679 Uebermuth Mar. 14, 1933 2,071,965 Biermanns Feb. 23, 1937 2,144,372 Haller et al Jan. 17, 1939 2,221,720 Prince Nov. 12, 1940 2,228,588 Ray Jan. 14, 1941 2,260,188 Milliken Oct. 21, 1941 2,279,536 Thommen Apr. 14, 1942 2,310,905 Blandford Feb. 9, 1943 

